Connect with TRB

This guide provides guidance for the design of horizontal curves on new highway sections and for the reconstruction and upgrading of existing curves on two-lane rural roads. Information is also provided in this guide for computing the expected benefits and costs for a variety of curve improvements, such as curve flattening, roadway widening, providing spiral transitions to curves, improving superelevation, sideslope flattening, and other roadside improvements. Thus, this guide should be useful to highway designers and safety officials responsible for the design of 3R projects, improvements to high-hazard locations, and highway reconstruction as it relates to horizontal curves. The accident relationships and basic project cost data contained in this guide resulted from research conducted for the Federal Highway Administration. FHWA research report FHWA-RD-90-021, entitled "Cost Effective Geometric Improvements for Safety Upgrading of Horizontal Curves, Volume I, Final Report" (TRIS 603210), contains the major results and conclusions of the study.